I. Field of the Invention
The present invention relates to high speed data networkinq in telecommunications and, more particularly, to a terminal adapter for allowing data terminal equipment (DTE) access both the frame relay and Switched Multimegabit Data Service (SMDS) high speed data services without the additional requirement of service-specific software and hardware in the customer premises equipment (CPE).
II. Prior Art
Over the past decade, many businesses, through growth and mergers, have dispersed their locations across the country and, in many cases, around the world. In the various business locations, local area networks (LANs) are used for interconnecting groups of people using PCs and workstations. As the popularity of LANs increases, so does the need for the interconnection of those LANs located across the country and around the world.
But as the size and geographic dispersement of these private networks grow, the interconnect expense increases. The cost and complexity of building and managing these private networks increase exponentially as more equipment, facilities and expertise is required.
Switched multimegabit data service (SMDS) and frame relay (FR) services are fairly new alternatives that can be used by public network operators to switch data through the network. Frame relay and SMDS, both "fast packet" multiplexing specifications, are designed to create more efficient wide area networks (WANs) by permitting users to access only the amount of bandwidth they need for a given application. 1n addition, both frame relay and SMDS have been recognized as being able to improve LAN networking solutions by standardizing LAN interconnection techniques and by reducing the number of required leased lines in a network.
This, however, is where the similarities between the two services ends. For example, frame relay is a "connection-oriented" protocol. It establishes a logical connection for the duration of the call, and it is initially being implemented as a permanent virtual circuit (PVC) service. In contrast, SMDS, which has adopted the IEEE 802.6 protocol, presently uses a "connectionless" protocol, meaning it doesn't set up a logical, ongoing connection for the duration of the call.
Another major difference between frame relay and SMDS is in the packets themselves. Frame relay packets, called frames, are variable in size--each frame in a frame relay network may be a different length from any other. SMDS packets, called cells, have a fixed size of 53 octets, which are eight-bit groups of data.
Furthermore, frame relay specifications define connections of speeds of 56 kbps to 1.5 Mbps, whereas SMDS describes speeds ranging from 1.5 to over 30 Mbps.
Although it is not clear as to which service, or both, the public networks will offer in the long-term, it is apparent that the network users should to be prepared to use either, or both, of the services. The service subscriber uses a communications product (DTE), such as a communications controller, a router, or a channel extender to access the frame relay and SMDS services. A terminal adapter (TA) is used to interface the DTE to the network. Because the mechanism and protocol to access these services are so strikingly different, a separate communications adapter (used to interface the DTE to the terminal adapter) and a separate terminal adapter are needed in order to access both of these services. This is shown in FIG. 1.
For instance, in order to access the frame relay network 10, a subscriber having customer premises equipment (CPE) 11 comprising a DTE 12 having a frame relay communications adapter 14 for interfacing with a frame relay terminal adapter 16. Presently, the accepted protocols for exchanging communication between the frame relay communications adapter 14 and the frame relay terminal adapter 16 is RVX (or RS 449, V.35, or X.21 type interface protocols). The DTE 12 and the frame relay communications adapter 14 comprise a "native" frame relay DTE 15. Similarly, the frame relay terminal adapter 16 is needed for communicating over the frame relay network 10 utilizing Link Access Procedure-D (LAPD), a protocol that originated in Integrated Services Digital Network (ISDN) standards.
With regard to a SMDS network 10', the subscriber must have a CPE 11' comprising a DTE 12, an SMDS communications adapter 14', and an SMDS terminal adapter 16' to employ the accepted interface protocol, the High Speed Serial Interface (HSSI). The DTE 12 and the SMDS communications adapter 14' comprise a native SMDS DTE 15'. The SMDS terminal adapter 16' communicates over the SMDS network 10' which has adopted the IEEE 802.6 protocol that supports packet voice/video services, as well as data transfer.
Because of evolutionary considerations, such as interface and protocol standardization and equipment availability, frame relay and SMDS will have to co-exist. Thus, it is desirable to have a CPE comprising a single terminal adapter which, on the terminal side, will interface with the subscriber's DTE and communications adapter and, on the network side, will interface with either an SMDS or a frame relay network.